The present invention relates to a lathe machine for turning wheel sets, especially sets of railroad wheels. Such milling machines operate in the manner of a lathe for reprofiling wheel sets and comprise roller means for driving and/or supporting a wheel set at the circumference thereof and at the wheel surface facing axially inwardly. An axially inwardly facing wheel surface faces the respectively axially inwardly facing surface of the other wheel forming a set. A wheel set has a common rotational axle. Machines of the above described type are known in the art and are described, for example, in Polish Pat. No. 78,173 or in German Patent Publication (DE-AS) 2,424,305.
Polish Pat. No. 78,173 discloses a wheel set milling machine or lathe which is referred to as an underfloor milling machine because its primary components are installed below the floor level of a machine shop. Such a machine comprises first roller means arranged for contacting the circumference of a wheel of a wheel set and second roller means arranged for contacting the inwardly facing surface of the wheels of a set, whereby at least the circumference contacting roller means drive the wheels of a set and whereby the inwardly facing surface contacting rollers are supposed to provide an alignment and guidance in the axial direction of the wheel set. The axial direction of a wheel set in this context is simultaneously the rotational axis of such a wheel set. In this prior art machine one set of rollers contacting an inwardly facing lateral wheel surface is supported in a rigid position while the other corresponding roller set which contacts the opposite inwardly facing lateral wheel surface is adjustable by hydraulic means. This type of arrangement has the inherent drawback that the wheel disks could be bent apart in the axial direction by the hydraulic adjustment of one of the second roller means so that when the wheel set is reprofiled a distorted profile may result. Another drawback of this type of arrangement is seen in that the opposite, rigidly positioned second roller set contacting an inner lateral wheel surface does not always provide the required counter support for the wheels, especially where the loads resulting from the reprofiling should vary. Thus, it is possible that the wheel set is subject to lateral excursions during the milling or machining or turning operation which again would result in an unsatifactory reprofiling operation.
The roller arrangement as disclosed in German Patent Publication 2,424,305 is not at all capable of taking up externally applied axially effective forces.
During the machining or milling operation substantially three types of axial forces are effective in the axial direction of a wheel set. The first type of axial force components is caused by the frictional forces which may result due to the fact that the rotational axes of the rollers contacting the circumference of the wheels do not extend precisely in parallel relative to one another. The second type of axial force components is caused by the geometrical shape of the instantaneous point of contact between the wheel surface and the respective roller which changes as the wheel rotates. The third type of axial force components comprises force components resulting from the cutting force. The just enumerated axial force components are effective to a substantial extent in a cumulative manner so that the total axial force may be rather substantial. Further, the just enumerated forces causing the axial force components cannot be measured in an economical way with regard to their size and direction. Thus, it has been common practice heretofore that the size of the required counterforce has been determined on the basis of empirical values. However, such empirical values are not satisfactory under all operating conditions and are therefore disadvantageous.